This invention relates generally to implantable devices for interventional therapeutic treatment or vascular surgery, and more particularly concerns a stretch resistant therapeutic device such as an embolic or vasoocclusive coil and an apparatus for release and deployment of the stretch resistant therapeutic device within a patient's vasculature.
The art and science of interventional therapy and surgery has continually progressed towards treatment of internal defects and diseases by use of ever smaller incisions or access through the vasculature or body openings, in order to reduce the trauma to tissue surrounding the treatment site. One important aspect of such treatments involves the use of catheters to place therapeutic devices at a treatment site by access through the vasculature. Examples of such procedures include transluminal angioplasty, placement of stents to reinforce the walls of a blood vessel or the like, and the use of vasoocclusive devices to treat defects in the vasculature.
One specific field of interventional therapy that has been able to advantageously use recent developments in technology is the treatment of neurovascular defects. As smaller and more capable structures and materials have been developed, treatment of vascular defects in the human brain which were previously untreatable or represented unacceptable risks via conventional surgery have become amenable to treatment. One type of non-surgical therapy that has become advantageous for the treatment of defects in the neurovasculature has been the placement by way of a catheter of vasoocclusive devices such as embolic coils in a damaged portion of a vein or artery.
Vasoocclusive devices are therapeutic devices that are placed within the vasculature of the human body, typically via a catheter, to form an embolus to block the flow of blood through a vessel making up that portion of the vasculature, or within an aneurysm stemming from the vessel. The vasoocclusive devices can take a variety of configurations, and are generally formed of one or more elements that are larger in the deployed configuration than when they are within the delivery catheter prior to placement. One widely used vasoocclusive device is a helical wire coil having a deployed configuration which may be dimensioned to engage the walls of the vessels. One anatomically shaped vasoocclusive device that forms itself into a shape of an anatomical cavity such as an aneurysm and is made of a pre-formed strand of flexible material that can be a nickel-titanium alloy is known from U.S. Pat. No. 5,645,558, which is specifically incorporated by reference herein. That vasoocclusive device comprises one or more vasoocclusive members wound to form a generally spherical or ovoid shape in a relaxed state. The vasoocclusive members can be a helically wound coil or a co-woven braid formed of a biocompatible material, and the device is sized and shaped to fit within a vascular cavity or vesicle, such as for treatment of an aneurysm or fistula. The vasoocclusive member can be first helically wound or braided in a generally linear fashion, and is then wound around an appropriately shaped mandrel or form, and heat treated to retain the shape after removal from the heating form. Radiopacity can be provided in the vasoocclusive members by weaving in synthetic or natural fibers filled with powdered radiopaque material, such as powdered tantalum, powdered tungsten, powdered bismuth oxide or powdered barium sulfate.
The delivery of such vasoocclusive devices can be accomplished by a variety of means, including via a catheter through which the device is pushed by a pusher to deploy the device. The vasoocclusive devices, which can have a primary shape of a coil of wire that is then formed into a more complex secondary shape, can be produced in such a way that they will pass through the lumen of a catheter in a linear shape and take on a complex shape as originally formed after being deployed into the area of interest, such as an aneurysm. A variety of detachment mechanisms to release the device from a pusher have been developed and are known in the art.
Vasoocclusive coils made of platinum, gold, and other ductile materials will easily deform from their coil shape under tension, causing a potentially dangerous situation when the coil is partially in an aneurysm and partially stretched in the delivery catheter. If it is determined that the coil is improperly placed, or is too large, the coil will need to be moved or replaced. However, at this stage of the procedure, the coil can no longer be pushed, and must be slowly retracted out of the catheter as a wire. If during this procedure the coil breaks, an additional procedure must be performed to remove the coil extending out of the aneurysm. It would be desirable to reinforce such vasoocclusive coils to provide stretch resistance to the coils to reduce the risk of the coils breaking, particularly during withdrawal of a coil for relocation or replacement, in order to provide a safety factor during retraction of soft or otherwise easily stretchable coils. It would also be desirable to minimize the increase of stiffness caused by reinforcement of the coils after the coils are released in deployment of the coils in an aneurysm so that the coils can freely transform to a desired secondary shape and conform to the dimensions of the location being treated. The present invention meets these and other needs.